1. Field of the Invention
This invention relates to a method of and an apparatus for preventing the emission of dioxins in an incineration facility, particularly, refuse incineration facility having a boiler.
2. Related Art
In a starting operation of a conventional refuse incineration facility having a boiler (see FIG. 1), an auxiliary burner was used, or refuse was directly burned in order to raise the temperature of an incinerator a and the temperature of boiler water in the boiler b. Low-temperature combustion gas, produced at an initial stage of this starting operation, inflicts damage, such as low-temperature corrosion, to an exhaust gas treatment facility c, and therefore it is a common practice to discharge this combustion gas via a by-pass duct d and a stack f, thus causing the exhaust gas to by-pass the exhaust gas treatment facility c (see thick arrows in FIG. 1).
At this time, there is a possibility that dust, containing hazardous substances, such as dioxins, remaining in the incinerator a and the boiler b, or highly-concentrated dioxins, produced during the starting operation of the incinerator a, deposit on an exhaust gas passage e and the stack f, provided downstream of the exhaust gas treatment facility c, to contaminate these portions, and there is also a possibility that semi-volatile precursors deposit and remain on these portions.
When such contamination substances are deposited and remain, there is a fear that after the steady operation of the incinerator a is started, these substances are emitted as gaseous dioxin or as dioxine adsorbed by particle-like dust, and are contained in the exhaust gas passed through the exhaust gas treatment facility c, and then are discharged via the stack f.
For example, in order to avoid damage due to dew condensation in a bag filter serving as the exhaust gas treatment facility c, it was necessary to discharge the gas via the by-pass duct d until the temperature of the gas rose to 120 to 130.degree. C.
As a result, the exhaust gas, though for a short period of time, continued to be discharged through the by-pass duct d until the temperature rose to a level at which the exhaust gas treatment facility c became usable, and this could form one of the causes of the increased dioxin emission concentration.